Moving magnet motors

ABSTRACT

An apparatus includes a load, a lever that is coupled to the load, and an electric motor that is coupled to the lever for driving the lever in oscillatory, rotary motion about a pivot axis. The electric motor includes an armature and a stator. The armature is coupled to the lever and includes a permanent magnet. The stator defines an air gap within which the armature is disposed. The stator is configured for creating magnetic flux across the air gap for the permanent magnet to interact with, thereby to drive motion of the load. The electric motor is configured such that substantially no detent forces (a/k/a cogging forces) are generated between the stator and the permanent magnet as the lever is driven by the motor.

BACKGROUND

This disclosure relates to moving magnet motors, and more particularlyto apparatus (e.g., a loudspeaker) in which a moving magnet motor isutilized to drive a mechanical load (e.g., an acoustic diaphragm).

SUMMARY

This disclosure is based, in part, on the realization that a movingmagnet motor can utilize a single, common stator for driving pluralarmatures. Such a moving magnet motor can advantageously be employed inan apparatus, such as a loudspeaker, for driving a mechanical load, suchas an acoustic diaphragm. This disclosure is also based, in part, on therealization that a moving magnet motor can be configured to drive a loadwithout generating detent forces (a/k/a cogging forces).

In one aspect, an apparatus includes at least one load and a pluralityof armatures, each including a permanent magnet, which are coupled tothe at least one load to cause the at least one load to move. Theapparatus also includes a common stator that defines an air gap withinwhich the plurality of armatures is disposed. The common stator isconfigured for creating magnetic flux across the air gap for thearmatures to interact with, thereby to drive motion of the at least oneload.

Implementations can include one or more of the following figures.

In some implementations, the stator includes at least one core of highmagnetic permeability material defining at least one air gap withinwhich the armatures reside. A pair of coils are wrapped around the atleast one core for carrying current to generate magnetic flux across theat least one air gap for the armatures to interact with.

In certain implementations, the stator includes a pair of cores of highmagnetic permeability material, the cores together defining the air gap.The stator also includes a pair of coils. Each of the coils is wrappedaround one of the cores for carrying current to generate magnetic fluxacross the air gap.

In some implementations, the stator comprises no more than two coils.

In certain implementations, the coils collectively include no more thanfour end turns.

In some implementations, the plurality of armatures are configured topivot about respective pivot axes.

In certain implementations, the plurality of armatures are configured tomove in a linear motion.

In some implementations, the apparatus includes a pair of levers whichcouple the armatures to the at least one load for transmittingrotational motion of the armatures to the at least one load to cause theat least one load to move.

In certain implementations, the levers are configured and arranged forrotation in opposite directions of rotation relative to each other.

In some implementations, the levers are arranged to move the at leastone load in a pistonic motion.

In certain implementations, the apparatus is a loudspeaker.

In some implementations, the at least one load includes an acousticdiaphragm.

In certain implementations, the apparatus includes an enclosure and asurround that connects the acoustic diaphragm to the enclosure. A bottomwall of the enclosure includes a recess that is arranged and configuredto accommodate downward motion of the armatures.

In some implementations, the stator is mounted to the bottom wall of theenclosure.

In certain implementations, the acoustic diaphragm is displaceablebetween a fully extended position in which the acoustic diaphragmextends outwardly away from the enclosure, and a fully retractedposition, in which the acoustic diaphragm is drawn inward towardsenclosure. In the fully retracted position, a lower edge of the acousticdiaphragm overlaps at least a portion of the armatures such that thearmatures are at least partially tucked into the acoustic diaphragm.

In some implementations, the armatures and the stator are positionedadjacent to and completely within the footprint of the acousticdiaphragm.

In certain implementations, the armatures are configured to moverelative to each other.

Another implementation features a method that includes passingelectrical current through coils of a common stator to generate magneticflux across an air gap which a plurality armatures interact with causingthe armatures to move, and thereby driving motion of at least one loadcoupled to the plurality of armatures. Each of the armatures includes apermanent magnet, disposed within the air gap, which interacts with themagnetic flux.

Implementations may include any of the above features and/or thefollowing.

In some implementations, driving motion of the at least one loadincludes driving motion of an acoustic diaphragm.

In certain implementations, driving motion of the at least one loadincludes driving the at least one load in a pistonic motion.

In some implementations, driving motion of the at least one loadincludes driving the plurality of armatures such that the armatures moverelative to each other.

In certain implementations, driving motion of the at least one loadincludes driving oscillatory, arcuate motion of a pair of levers.

In some implementations, driving oscillatory, arcuate motion of the pairof levers includes driving the levers in opposite directions of rotationrelative to each other.

In another aspect, a loudspeaker includes an acoustic diaphragm, a firstarmature, and a first lever mechanically coupling the first armature andthe acoustic diaphragm and configured such that motion of the firstarmature causes the first lever to pivot about a first pivot axis. Theloudspeaker also includes a second armature and a second levermechanically coupling the second armature and the acoustic diaphragm andconfigured such that motion of the second armature causes the secondlever to pivot about a second pivot axis. A common stator is providedfor creating magnetic flux for the first and second armatures tointeract with, thereby to drive motion of the at least one load.

Implementations may include any of the above features and/or thefollowing.

In certain implementations, the common stator defines an air gap withinwhich the first and second armatures are disposed, and the stator isconfigured to create magnetic flux across the air gap for the first andsecond armatures to interact with.

In some implementations, the common stator defines a first air gapwithin which the first armature is disposed, and a second air gap withinwhich the second armature is disposed. The stator is configured tocreate magnetic flux across the first and second air gaps for the firstand second armatures, respectively, to interact with.

In certain implementations, the levers are configured and arranged forrotation in opposite directions of rotation relative to each other.

In some implementations, the levers are arranged to move the load in apistonic motion.

In certain implementations, the first and second levers are configuredas first class levers.

In some implementations, the first and second levers are configured assecond class levers.

Another aspect provides an apparatus includes a load, a lever that iscoupled to the load, and an electric motor that is coupled to the leverfor driving the lever in oscillatory, rotary motion about a pivot axis.The electric motor includes an armature and a stator. The armature iscoupled to the lever and includes a permanent magnet. The stator definesan air gap within which the armature is disposed. The stator isconfigured for creating magnetic flux across the air gap for thepermanent magnet to interact with, thereby to drive motion of the load.The electric motor is configured such that substantially no detentforces (a/k/a cogging forces) are generated between the stator and thepermanent magnet as the lever is driven by the motor.

Implementations may include any of the above features and/or thefollowing.

In some implementations, the stator defines a first pole which includesa first pair of opposed pole faces, and a second pole which includes asecond pair of opposed pole faces. The air gap separates the first pairof opposed pole faces, and the gap separates the second pair of opposedpole faces.

In certain implementations, the stator is configured to generatemagnetic flux which passes in a first direction between the first pairopposed pole faces, while, at the same time, passing in a seconddirection, opposite the first direction, between the second pair ofopposed pole faces.

In some implementations, the stator is configured to generate magneticflux which passes across the air gap in two opposing directions at thesame time.

In certain implementations, the stator includes a pair of cores of highmagnetic permeability material, and a pair of coils. The cores togetherdefine a first pole, a second pole, and an air gap within which thepermanent magnet is suspended. Each coil is wrapped around one of thecores for carrying current to generate magnetic flux across the air gapfor the permanent magnet to interact with.

In some implementations, the lever is coupled to the load such thatoscillatory, rotary motion of the lever moves the load in a pistonicmotion.

In certain implementations, the apparatus is a loudspeaker, and the loadis an acoustic diaphragm.

In some implementations, the loudspeaker has a sealed box construction.

In certain implementations, the lever is coupled to the acousticdiaphragm such that oscillatory, rotary motion of the lever moves theacoustic diaphragm in a pistonic motion.

In yet another aspect, a loudspeaker includes an acoustic diaphragm, andan electric motor coupled to the acoustic diaphragm for driving motionof the acoustic diaphragm. The electric motor includes a stator, and anarmature. The stator includes a pair of cores of high magneticpermeability material, and a pair of coils. The cores together define afirst pole, a second pole, and an air gap separating opposed faces ofthe first and second poles. Each of the coils is wrapped around one ofthe cores for carrying current to generate magnetic flux across the airgap. The armature includes a single permanent magnet, the armaturedisposed within the air gap in non-contacting relationship with thestator and supported to allow the permanent magnet to interact withmagnet flux in the air gap for moving the armature between the first andsecond poles.

Implementations may include any of the above features and/or thefollowing.

In some implementations, the stator is configured to generate magneticflux which passes across the air gap in two opposing directions at thesame time.

In certain implementations, the stator is configured to generatemagnetic flux which passes in a first direction between opposed polefaces of the first pole, while, at the same time, passing in a seconddirection, opposite the first direction, between opposed pole faces ofthe second pole.

In some implementations, the stator is configured to generate magneticflux across the air gap such that the permanent magnet is attracted toone of the first and second poles and is repelled by the other one ofthe first and second poles.

Implementations can provide one or more of the following advantages.

In some Implementations, the use of a single, common stator for drivingmultiple armatures can help to reduce the number of parts in anapparatus. Such a reduction in parts can provide packaging andmanufacturing benefits. For example, a reduction in the number of partscan lead to a corresponding reduction in manufacturing steps with lessparts requiring assembly. A reduction in parts can also help reduce orfree up packaging space, thereby possibly reducing overall package sizeand/or freeing up space for other component parts.

In certain implementations, the use of a single, common stator fordriving multiple armatures can offer overall lower electricalresistance, e.g., as compared to multi-stator arrangements.

In some implementations, the use of a single, common stator for drivingmultiple armatures can offer better magnetic performance relative toinput power, e.g., as compared to multi-stator arrangements.

In certain implementation, providing a moving magnet motor with asubstantially zero detent configuration can help to reduce powerconsumed by the motor when utilized to drive a load. More specifically,a substantially zero detent configuration can substantially eliminatedetent forces (a/k/a cogging forces) which the motor would otherwiserequire additional power to overcome.

Other aspects, features, and advantages are in the description,drawings, and claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a top plan view of a loudspeaker that employs a moving magnetmotor which includes a single, common stator for driving a pair ofarmatures, which in turn drive an acoustic diaphragm.

FIG. 1B is a cross-sectional side view of the loudspeaker of FIG. 1A,taken along line 1B-1B.

FIG. 2A illustrates oscillatory, arcuate movement of the armatures andpistonic movement of an acoustic diaphragm of the loudspeaker of FIG.1A.

FIGS. 2B and 2C are cross-sectional side views of the loudspeaker ofFIG. 1A showing the acoustic diaphragm in a fully extended position anda fully retracted position, respectively.

FIG. 3A is a perspective view of the common stator of the loudspeaker ofFIG. 1A.

FIG. 3B is a cross-sectional view of a substantially zero detent motorstructure, formed by the common stator and armatures of the loudspeakerof FIG. 1A, illustrating one of the armatures interacting with magneticflux across an air gap formed by the stator.

FIG. 4A is a top view of the common stator of FIG. 3A.

FIG. 4B is a top view of a multi-stator arrangement for comparison withthe implementation shown in FIG. 4A.

FIG. 5 is a perspective view of a pair of levers which support thearmatures of the loudspeaker of FIG. 1A.

FIG. 6A is a top plan view of another implementation of a loudspeakerthat employs a moving magnet motor which includes a single, commonstator for driving a pair of armatures in a linear motion.

FIG. 6B is a cross-sectional side view of the loudspeaker of FIG. 6A,taken along line 6B-6B.

FIG. 7 is a cross-section side view of a loudspeaker that employs amoving magnet motor which includes a single, common stator that iscapable of driving more than two armatures which drive respective loads.

FIG. 8A is a front view of an alternative implementation of a movingmagnet motor (shown with a lever arm in an air gap of the motor) thatcan be employed with the loudspeaker of FIG. 1A and/or the loudspeakerof FIG. 6A.

FIG. 8B is cross-sectional side view of the moving magnet motor of FIG.8A (shown with a pair of lever arms in the air gap), taken along line8B-8B.

FIG. 9A is a top plan view of a loudspeaker that employs a moving magnetmotor which includes a single, common stator for driving a pair ofarmatures, each of which drives a separate diaphragm.

FIG. 9B is a cross-sectional side view of the loudspeaker of FIG. 9A,taken along line 9B-9B.

FIG. 10A is a perspective view of another implementation of a movingmagnet motor having a common stator that defines plural air gaps (shownwith levers in the air gaps).

FIG. 10B is a front view of the moving magnet motor of FIG. 10A.

FIG. 10C is a cross-sectional side view of the moving magnet motor ofFIG. 10B, taken along line 10C.

FIG. 11 is a cross-sectional side view of an implementation of aloudspeaker having levers arranged in a second class leverconfiguration.

FIG. 12A is a top plan view of a loudspeaker that employs a movingmagnet motor having a substantially zero detent topology for driving anarmature, which, in turn, drives an acoustic diaphragm.

FIG. 12B is a cross-sectional side view of the loudspeaker of FIG. 1A,taken along line 12B-12B.

FIG. 13 illustrates oscillatory, arcuate movement of the lever andpistonic movement of an acoustic diaphragm of the loudspeaker of FIG.12A.

FIG. 14 is a perspective view of a lever, of the loudspeaker of FIG.12A, including an armature for the moving magnet motor.

FIG. 15 is a perspective view of a stator of the moving magnet motor ofthe loudspeaker of FIG. 12A.

FIG. 16A is a top view of the armature and stator of the moving magnetmotor of the loudspeaker of FIG. 12A.

FIG. 16B is an end view of the armature and stator from the movingmagnet motor of FIG. 12A illustrating the armature interacting withmagnetic flux across an air gap formed by the stator.

DETAILED DESCRIPTION

Referring to FIGS. 1A and 1B, an apparatus, in this example aloudspeaker 100, includes a mechanical load, in this example an acousticdiaphragm 102 (e.g., a cone type speaker diaphragm, also known simply asa “cone”), that is mounted to an enclosure 104, which may be metal,plastic, or other suitable material, by a surround 106, which functionsas a pneumatic seal and as a suspension element. For example, in someinstances the surround 106 is mounted to a frame 108 and the frame 108is connected to the enclosure 104. The loudspeaker 100 also includes apair of levers (i.e., first and second levers 110 a, 110 b) each ofwhich couple an associated armature 112 to the acoustic diaphragm 102for transmitting motion of the armatures 112 to the acoustic diaphragmto cause the acoustic diaphragm 102 to move, relative to the enclosure104.

Each of the armatures 112 includes a single permanent magnet 113.Notably, both of the armatures 112 are driven by a single, common stator113, which provides a magnetic flux for the permanent magnets 113 ofboth of the armatures 112 to interact with, thereby to drive motion ofthe acoustic diaphragm. In the illustrated example, the stator 114 issecured to a bottom wall 116 of the enclosure 104 (e.g., with anadhesive). Alternatively or additionally, the stator 114 could beaffixed to the frame 108.

Each of the levers 110 a, 110 b is pivotally connected to a mechanicalground reference, such as the enclosure 104 or the frame 108 of theloudspeaker 100 such that the levers 110 a, 110 b move in an arcuatepath about respective pivot axes 118 a, 118 b.

The armatures 112 and the stator 114 are positioned beneath the acousticdiaphragm 102 with the pivot axes 118 a, 118 b being arranged outboardof the armatures 112. That is, the armatures 112 are disposed betweenthe pivot axis 118 a of the first lever 110 a and the pivot axis 118 bof the second lever 110 b. The armatures 112 and the stator 114 arebetween the acoustic diaphragm 102 and the bottom wall 116 of theenclosure 104, and substantially within the footprint of the acousticdiaphragm 102, as defined by the outer peripheral edge of the acousticdiaphragm 102. In some cases, this arrangement can be beneficial, from apackaging perspective, compared to arrangements in which moving magnetmotors are arranged alongside the outer perimeter of the acousticdiaphragm 102.

Referring now to FIGS. 2A through 2C, the levers 110 a, 110 b, incombination with the interaction between the armatures 112 and thestator 114 (not shown in FIG. 2A), move the acoustic diaphragm 102 in apistonic motion (as indicated by arrow 120, FIG. 2A). For very smallmotion (e.g., rotation (arrows 122, FIG. 2A) of the levers 110 a, 110 bover a very small angle θ (e.g., less than 0.1 radians), there isnegligible relative lateral motion (arrow 124, FIG. 2A) between theacoustic diaphragm 102 and the connection points of the levers 110 a,110 b to the acoustic diaphragm 102. Thus, for configurations in whichonly slight rotation of the levers 110 a, 110 b is required to achievemaximum excursion of the acoustic diaphragm 102, connectors 126 thatconnect the levers 110 a, 110 b to the acoustic diaphragm 102 may beimplemented as simple hinges that merely allow for relative rotation,with little or no relative lateral movement.

As the angle of rotation θ of the levers 110 a, 110 b increases so doesthe relative lateral movement between the acoustic diaphragm 102 and theconnection points of the levers 110 a, 110 b to the acoustic diaphragm102. To accommodate such motion, connectors 126 which allow for at leasttwo-degrees of movement (i.e., relative rotational movement and relativelateral movement) can be used to connect the levers 110 a, 110 b to theacoustic diaphragm 102. In this regard, each connector 126 can beimplemented as a linkage with a hinge on each end, a flexure (such as ametal strip), an elastomeric connection (such as a block of elastomer),or some combination thereof. The levers 110 a, 110 b drive the acousticdiaphragm 102 between a fully extended position (see FIG. 2B), in whichthe acoustic diaphragm 102 extends outwardly away from the enclosure104, and a fully retracted position (see FIG. 2C), in which the acousticdiaphragm 102 is drawn inward toward a chamber 128 of the enclosure 104.The total, peak-to-peak excursion distance (d1) can be designed to beanything over a wide range (e.g., about 1 mm to about 30 mm (e.g., 4mm)) and can be somewhat dependent on transducer size constraints, andthe angle of rotation θ is about 2 degrees to about 20 degrees (e.g., 6degrees)

In the fully extended position (FIG. 2B), the armatures 112 are rotateddownward toward the bottom wall 116 of the enclosure 104. In some cases,the armatures 112 may extend beyond the profile of the stator 114 whenthe acoustic diaphragm 102 is in its fully extended position. Toaccommodate this motion of the armatures 112, a recess 130 may beprovided in the bottom wall 116 of the enclosure 104 to afford greaterclearance.

In the fully retracted position (FIG. 2C), the armatures 112 rotateupwards towards the acoustic diaphragm 102. In some cases, the clearance(d2) between the armatures 112 and the acoustic diaphragm 102 is lessthan 1 mm (e.g., within 0.5 mm) in the fully retracted position. In somecases, the armatures 112 at least partially tuck underneath the acousticdiaphragm 102 such that the lower edge 132 of the acoustic diaphragm 102extends below the highest portion of the armatures 112 in the retractedposition. This can allow for a better utilization of the availablevolume.

An exemplary implementation of the stator 114 is illustrated in FIGS.3A, 3B, and 4A. As shown in FIGS. 3A, 3B, and 4A, the stator 114includes a pair of U-shaped cores 140 of high magnetic permeabilitymaterial, such as soft iron. Each core 140 includes a first leg 142, asecond leg 144, and a back portion 146 that extends between the firstand second legs 142, 144. The first leg 142, the second leg 144, and theback portion 146 can be formed as separate components that are fastenedtogether or can be integrally formed out of a common piece of material.Each core 140 also includes a coil 148 of electrically conductivematerial wound about the back portion 146 of the associated core 140between the first and second legs 142, 144. In this regard, the cores140 are said to include a backside winding, which, by keeping the coils148 out of the vertical stack-up of components, helps to provide thestator 114 with a low profile height for an overall lower profileloudspeaker 100. The cores 140 are arranged adjacent to each other anddefine an air gap 150 therebetween, which is substantially filled by thearmatures 112. The air gap 150 is a single, common air gap that isshared by both armatures 112.

Notably, the cores 140 together define a pair of poles 147 a, 147 b forthe single permanent magnet 113 of each armature 112 to interact with.The first legs 142 of the cores 140 form a first pole 147 a with a firstpair of opposed pole faces 149 a, and the second legs 144 form a secondpole 147 b with a second pair of opposed pole faces 149 b. The air gap150 separates the first pair of opposed pole faces 149 a, as well as thesecond pair of opposed pole faces 149 b.

The coils 148 are arranged so that the magnetic fields produced bycurrent flowing through them add constructively. Current in coils 148produces a magnetic flux across the air gap 150. As illustrated in FIG.3B, the current in the coils 148 produces magnetic flux which passesacross the air gap 150 in two opposing directions at the same time. Thatis, magnetic flux 151 produced by the current in the coils 148 passes ina first direction between the first pair opposed pole faces 149 a,while, at the same time, passing in a second direction, opposite thefirst direction, between the second pair of opposed pole faces 149 b.The flow of current in the coils 148 is reversed to reverse thedirection of the magnetic flux. The magnetic flux interacts with thepermanent magnets 113 of the armatures 112 to drive the motion of theacoustic diaphragm 102. The flow of current in the coils 148 can berepeatedly reversed to drive the armatures 112 in oscillatory motion.The combination of the armatures 112, the cores 140, and the coils 142form a moving magnet motor. The interaction of the magnetic field in theair gap 150 due to current flowing in the coils 148 and magnetic fieldsof the magnets 113 apply force to the magnets 113 in a non-contactmanner. Force from the magnets 113 is coupled structurally to the levers110 a, 110 b and ultimately to the acoustic diaphragm 102.

The two pole stator/one magnet (per armature) arrangement of the movingmagnet motor provides a substantially zero detent topology. That is,with this two pole/one magnet configuration substantially no cogging(detent) forces are generated between the stator 114 and the individualpermanent magnets 113 as the levers 110 a, 110 b are driven inoscillatory rotary motion; i.e., the detent forces are less than 10% ofthe work needed to move the diaphragm 102 over its peak-to-peakexcursion distance (e.g., less than 5% of the work needed to move thediaphragm 102). This can help to minimize power consumption since themotor does not have to work to overcome its own detent forces. This canbe particularly beneficial where the loudspeaker 100 is configured as asealed box (i.e., where the enclosure 104 is sealed). In such sealed boxconfigurations, the motor needs to overcome the sum of the box stiffnessand the magnetic detent stiffness. Reducing the detent stiffness cansignificantly reduce the power needed to drive the motor.

For purposes of comparison, FIG. 4B illustrates an alternative,multi-stator arrangement in which a pair of stators 160 are arranged soas to drive two levers. In comparison to this multi-stator design (FIG.4B), the common stator 114 (FIG. 4A) offers a simpler design. Eventhough the cores 140 may be longer than the individual cores 162 of themulti-stator arrangement, the common stator 114 reduces the total numberof coils which can provide a design that is not only easier tomanufacture (e.g., because of the reduction in parts) but which can alsooffer overall lower electrical resistance, and better magneticperformance.

Comparing FIGS. 4A and 4B, the common stator 114 of FIG. 4A reduces thenumber of coils (i.e., two coils 148 in the arrangement of FIG. 4A vs.four coils 164 in the arrangement of FIG. 4B), which can help to reducethe overall resistance since wrapping two coils results in an overallshorter path length (despite the longer core length in the common statorarrangement) than the wrapping of four coils. That is, while the commonstator 114 is larger than each of the individual stators of themulti-stator arrangement for a given output, the perimeter around thelarger stator is shorter than the sum of the perimeters around the twosmaller stators. As a result, less wire is used in the common statorarrangement. The additional wire in the two stator arrangement addsresistance, inductance, weight, and cost.

The number of end turns is also reduced (i.e., four coil end turns 152in the arrangement of FIG. 4A vs. eight coil end turns 166 in thearrangement of FIG. 4B). This can provide for improved magneticperformance since the magnetic flux associated with the end turns do tonot couple as well into the core as does the flux associated with theinterior turns of the coils. Consequently, a significant amount of themagnetic flux from the end turns does not pass through the magnet and,thus, adds leakage inductance without driving the armatures 112. This inturn means it takes more amplifier power to produce the same motorpower. Reducing the number of ends turns can help to reduce thisinefficiency.

The common stator arrangement also offers a better utilization of space.More specifically, in the two stator arrangement of FIG. 4B, there isadditional space that is taken up by clearance(s) between the adjacentstators 160, which is not required in the common stator arrangement ofFIG. 4A. As a result, the common stator arrangement can leave more spacefor accommodating other elements, such as allowing for longer levers 110a, 110 b.

As shown in FIG. 5, each of the armatures 112 includes a magnet carrier170 which supports the permanent magnet 113. The magnets 113 can besecured in their respective magnet carriers 170 with an adhesive, amechanical interface, snap features, mold in place, or combinationsthereof, etc. The levers 110 a, 110 b can be formed of a metal, such asaluminum; a glass-filled plastic; or other suitable low mass highstiffness materials. In some cases, the magnet carrier 170 is formedintegrally with the associated lever 110 a, 110 b.

The magnets 113 are arranged such that like poles (north poles shown inFIG. 5) face the same core 140 of the stator 114, such that the magnets113 are polarized in the same direction in the air gap 150. In somecases, the magnets 113 are arranged in an underhung configuration wherethe magnets 113 are shorter than the depth of the air gap 150 in thez-direction (z-axis shown in FIG. 1B). In some applications, the magnets113 overshoot the air gap 150 at the extreme upward and extreme downwardpositions of the acoustic diaphragm 102. In some cases, the magnets 113are also overhung a distance (d3), e.g., about half the width of the airgap 150, along the x-axis (shown in FIG. 1B) to catch fringe flux.

Referring to FIG. 5, each of the levers 110 a, 110 b includes adiaphragm attachment point 171 (the lever resistance), where the leveris attached to the diaphragm (e.g., via a connector 126 (FIG. 2A)). Theattachment point 171 is positioned a lever length L1 away from the pivotaxis 118 a, 118 b (the lever fulcrum). Each of the levers 110 a, 110 balso has an associated force application point 172 (i.e., a point whereforce is effectively applied from the associated armature 112), whichrepresents the lever effort. In the illustrated example, the forceapplication point 172 is approximated at the center of the magnet 113.The force application point 172 is positioned a lever length L2 awayfrom the pivot axis 118 a, 118 b.

Generally, it can be preferable to minimize the angle of rotation of thelever 110 a, 110 b. Since the stroke is approximately the product of theangle of rotation of the lever 110 a, 110 b (in radians) and the leverlength L1, gaining length reduces the angle of rotation needed toachieve the same stroke. At very small angles, e.g., less than 0.15radians, the non-linearity of force-to-stroke is small enough to benegligible, but as the angle of rotation increases non-linearity offorce-to-stroke can start to introduce harmonic distortion issues.

The gear ratio L1/L2 can be set to optimize the application. In somesituations it may be better to raise the gear ratio to lower effectivemagnet mass relative to the cone. This might be the case if the conepressure is low (e.g., infinite baffle applications). On the other handit might be better to lower the gear ratio if the cone pressure load ishigh. (e.g., small sealed box applications)

Other Implementations

Although a few implementations have been described in detail above,other modifications are possible. For example, while an implementationof a loudspeaker has been described in which a common stator is arrangedto drive a pair of armatures in an arcuate, oscillatory motion, in someinstances, a common stator may be utilized to drive multiple armaturesin a linear motion. For example, FIGS. 6A and 6B illustrate animplementation in which a loudspeaker 200 includes an acoustic diaphragm202 that is mounted to an enclosure 204 by a surround 206 (e.g., via aframe 208). The loudspeaker 200 also includes a pair of armatures 212each of which includes a permanent magnet and each of which is coupledto the acoustic diaphragm 202 via an associated connecting arm 213 fortransmitting motion of the armatures 212 to the acoustic diaphragm tocause the acoustic diaphragm 202 to move, relative to the enclosure. Theconnecting arms 213 can be formed of a metal, such as aluminum; or aglass-filled plastic. The connecting arms 213 can be connected to thediaphragm with an adhesive.

Both of the armatures 212 are driven by the single, common stator 214,which provides a magnetic flux for both of the armatures to interactwith, thereby to drive motion of the acoustic diaphragm. The armatures212 and the stator 214 are positioned beneath the acoustic diaphragm 202and are within the footprint, as defined by the outer peripheral edge,of the acoustic diaphragm 202. The stator 214 drives the armatures 212in a linear, up-and-down motion (as indicated by arrow 215), which, inturn, drives the acoustic diaphragm 202 in a pistonic motion.

The stator 214 can have a structure as described above with regard toFIG. 3A. More specifically, the stator 214 can include a pair ofU-shaped cores 240 of high magnetic permeability material, such as softiron. Each core 240 carries a coil 248 of electrically conductivematerial wound about a back portion of the associated core 240. Thecores 240 are arranged adjacent to each other and define an air gap 250therebetween, within which the armatures 212 are disposed. The air gap250 is a single, common air gap that is shared by the armatures 212. Insuch cases, a suspension such as flexure (not shown) can be used to keepthe magnets centered between the cores 240 of the stator 214 to inhibitthe armatures 212 from crashing into the stator 214.

The coils 248 are connected (e.g., in series) and polarized so that themagnetic fields produced by current flowing through them addconstructively. Current in coils 248 produces a magnetic flux across theair gap 250. The magnetic flux interacts with the armatures 212 to drivethe motion of the acoustic diaphragm 202.

In the illustrated example, the stator 214 is secured to a bottom wall216 of the enclosure 204 (e.g., with an adhesive). To accommodate thedownward motion of the armatures 212, a recess 230 may be provided inthe bottom wall 216 of the enclosure 204 to afford greater clearance.

In some cases, the common stator can be used to drive more than twoarmatures. Alternatively or additionally, multiple armatures may beemployed to drive multiple loads. For example, FIG. 7 illustrates animplementation of an apparatus (e.g., a loudspeaker 200′) in which thecommon stator 214 (which can have a structure as described above withregard to FIG. 3A) is used to drive pistonic, oscillatory motion ofthree armatures 212 a, 212 b. 212 c, each of the armatures 212 a, 212 b,212 c being coupled to a separate load (e.g., separate acousticdiaphragms 202 a, 202 b, 202 c) via an associated connecting arm 213 a,213 b, 213 c. In such cases, a suspension such as flexure (not shown)can be used to keep the magnets centered between the cores 240 of thestator 214 to inhibit the armatures 212 a, 212 b, 212 c from crashinginto the stator 214.

In the example illustrated in FIG. 7, two of the acoustic diaphragms 202a, 202 b are arranged along a first side of the loudspeaker 200′ and aremounted to an enclosure 204, which may be metal, plastic, or othersuitable material, by respective surrounds (i.e., first and secondsurrounds 206 a, 206 b). In the illustrated example, the surrounds 206a, 206 b are mounted to the enclosure 204 via a first frame 208 a. Thatis, the surrounds 206 a, 206 b are mounted to the first frame 208 a andthe first frame 208 a is connected to the enclosure 204. A third one ofthe acoustic diaphragms 202 b is arranged along an opposite, second sideof the loudspeaker 200′ and is mounted to the enclosure 204 via a secondframe 208 b. The second frame 208 b may be separate from, coupled to, orintegral with the first frame 208 a.

Each of the armatures 212 a, 212 b, 212 c includes a permanent magnet217 a, 217 b, 217 c. The common stator 214 provides a magnetic flux forthe permanent magnets 217 a, 217 b, 217 c to interact with, thereby todrive motion of the acoustic diaphragms 202 a, 202 b, 202 c. The stator114 can be secured to the enclosure 204 and/or to one or both of theframes 208 a, 208 b.

The magnet 217 c of the center armature 212 c is positioned such thatits polarity is opposite that of the outer two armatures 212 a, 212 b sothat the center acoustic diaphragm 202 c is driven in a direction thatis opposite to a direction that the outer two acoustic diaphragms 202 a,202 b are driven. This can help to balance forces applied to theloudspeaker 200′.

FIGS. 8A and 8B illustrate another implementation of a moving magnetmotor having a common stator for driving plural armatures that can beused, e.g., in the loudspeakers of FIGS. 1A and 6A. The stator 314 ofFIGS. 8A and 8B includes a single C-shaped core 340 of high magneticpermeability material, such as soft iron. The core 340 includes a firstleg 342, a second leg 344, and a connecting portion 346 that extendsbetween the first and second legs 342, 344. The core 340 carries a firstcoil 348 a of conducting material wound about the first leg 342 and asecond coil 348 b of conducting material wound about the second leg 344.The first and second legs 342, 344 define an air gap 350 therebetween,within which armatures 312 (FIG. 8B) can be disposed. The air gap 350 isa single, common air gap that is shared by the armatures 312. Thearmatures 312 are each coupled to one of a pair of levers 310 a, 310 b,e.g., for transmitting arcuate motion (arrows 322) of the armatures 312(about pivot axes 318 a, 318 b) to a load (not shown) such as anacoustic diaphragm attached to the ends of the levers 310 a, 310 bopposite the armatures 312. In this implementation, the armatures 312each include a pair of magnets 313A, 313B having reversed polarity ofmagnetization. The coils 348 a, 348 b are connected and polarized sothat the magnetic fields produced by current flowing through them addconstructively. Current in coils 348 a, 348 b produces a magnetic fluxacross the air gap 350. The magnetic flux interacts with the armatures312 to drive the motion of the acoustic diaphragm.

While an implementation of an apparatus (e.g., a loudspeaker) has beendescribed in which a single, common stator is employed to drive plurallevers, which, in turn, drive a common mechanical load (e.g., aloudspeaker), in some implementations, a common stator may be employedto drive plural levers, each of which drive a separate load. Forexample, FIGS. 9A and 9B illustrate an implementation of a loudspeaker400 that includes a pair of acoustic diaphragms 402 each of which ismounted to an enclosure 404 (e.g., via a frame 408) by an associatedsurround 406. The loudspeaker 400 includes a pair of levers (i.e., firstand second levers 410 a, 410 b) each of which couple an associatedarmature 412 to one of the acoustic diaphragms 402, via connectors 426,for transmitting motion of the armatures 412 to the acoustic diaphragms402 to cause the acoustic diaphragms 402 to move, relative to theenclosure 404. Notably, both of the armatures 412 are driven by asingle, common stator 414, which provides a magnetic flux for both ofthe armatures 412 to interact with, thereby to drive motion of theacoustic diaphragm 402. The stator 414 can have a structure as describedabove with regard to FIG. 3A.

FIGS. 10A, 10B, and 10C illustrate yet another implementation of amoving magnet motor having a common stator for driving plural armaturesthat can be used, for example, in the loudspeakers discussed above. Thestator 514 of FIGS. 10A-10C includes a single core 540 of high magneticpermeability material, such as soft iron. The core 540 includes a firstleg 542, a second leg 544, and a connecting portion 546 that extendsbetween the first and second legs 542, 544. The core 540 carries a firstcoil 548 a of conducting material wound about the first leg 542 and asecond coil 548 b of conducting material wound about the second leg 544.

A center leg 547 extends upwardly from the connecting portion 546 into aregion between the first and second legs 542, 544 to define a pair ofair gaps 550 a and 550 b (FIG. 10B) therebetween. The moving magnetmotor includes a pair of armatures 512 each of which is disposed in anassociated one of the air gaps 550 a, 550 b. The armatures 512 are eachcoupled to one of a pair of levers 510 a, 510 b, e.g., for transmittingmotion of the armatures 512 to a load (not shown) such as an acousticdiaphragm attached to the ends of the levers 510 a, 510 b opposite thearmatures 512. The armatures 512 each include a pair of magnets 513A,513B having reversed polarity of magnetization.

The levers 510 a, 510 b are arranged to pivot about pivot axes 518 a,518 b. The interaction of the magnetic fields in the air gaps 550 a, 550b due to current flowing in the coils 548 a, 548 b and magnetic fieldsof the magnets 513 a, 513 b drive the levers 510 a, 510 b in arcuatemotions (arrows 522) of opposite directions relative to each other.

Although implementations have been described in which a moving magnetmotor that utilizes a common stator to drive multiple armatures isemployed for controlling displacement of an acoustic diaphragm in aloudspeaker, such moving magnet motors can be employed in otherapparatus. For example, a moving magnet motor that utilizes a commonstator to drive multiple armatures may be employed for controllingdisplacement of a diaphragm in a diaphragm pump. Alternatively, suchmotors can be employed to drive a piston in a piston pump.

While implementations have been described which include first classlever arrangements (i.e., arrangements in which the pivot axis (thelever fulcrum) is intermediate the armature/force application point (thelever effort) and the diaphragm attachment point (i.e., the point ofattachment between the lever and the diaphragm) which represents thelever resistance, other implementations are possible. For example, thelevers can be arranged in a second class lever configuration in whichthe point of attachment between the lever and the diaphragm isintermediate the pivot axis and the armature.

FIG. 11 illustrates an exemplary apparatus (e.g., a loudspeaker 600)which implements a second class lever configuration. The loudspeakerincludes an acoustic diaphragm 602 (a mechanical load), that is mountedto an enclosure 604 by a surround 606. The loudspeaker 600 also includesa pair of levers (i.e., first and second levers 610 a, 610 b) each ofwhich couple an associated armature 612 to the acoustic diaphragm 602for transmitting motion of the armatures 612 to the acoustic diaphragmto cause the acoustic diaphragm 602 to move, relative to the enclosure604.

Each of the armatures 612 includes a permanent magnet 613. Once again,both of the armatures 612 are driven by a single, common stator 614,which provides a magnetic flux for the permanent magnets 613 of both ofthe armatures 612 to interact with, thereby to drive motion of theacoustic diaphragm. Each of the levers 610 a, 610 b is pivotallyconnected to a mechanical ground reference, such as the enclosure 604 orthe frame 608 of the loudspeaker 600, such that the levers 610 a, 610 bmove in an arcuate path about respective pivot axes 618 a, 618 b.Notably, the pivot axes 618 a, 618 b are intermediate the respectiveforce application points (the armatures 612) and respective diaphragmattachment points 627.

While implementations have been described in which a moving magnet motorhaving a substantially zero detent configuration is utilized to drive apair of armatures and levers, in other implementations, a moving magnetmotor having a substantially zero detent configuration can be utilizedto drive a single armature and lever.

For example, referring to FIGS. 12A and 12B, a loudspeaker 700 includesan acoustic diaphragm 702 that is mounted to an enclosure 704, which maybe metal, plastic, or other suitable material, by a surround 706, whichfunctions as a pneumatic seal and as a suspension element. For example,in some instances the surround 706 is mounted to a frame 708 and theframe 708 is connected to the enclosure 704. The enclosure 704 may be asealed box enclosure, or a ported box enclosure.

In the example illustrated in FIGS. 12A and 12C, the loudspeaker 700includes a single lever 710 that is mechanically connected at one pointalong the lever 710 to the acoustic diaphragm 702 and at another pointalong the lever 710 to a moving magnet motor 712 having a substantiallyzero detent topology (i.e., the detent forces generated by the motor 712are less than 10% of the total work needed to move the acousticdiaphragm 702 over its peak-to-peak excursion distance).

The lever 710 is pivotally connected to a mechanical ground reference,such as the enclosure 704 or the frame 708, such that the lever 710moves in an arcuate path about a pivot axis 714 pivot axis 714. Asillustrated in FIG. 13, when an oscillatory force (arrow 716) is appliedto the lever 710 via the moving magnet motor 712 (FIG. 12A), the lever710 is driven in an arcuate path (arrow 717) about the pivot axis 714.The motion of the lever 710 is transferred to the acoustic diaphragm 702via the connection point, which causes the acoustic diaphragm 702 tomove along a path (arrow 718) between a fully extended position and afully retracted position. In some cases, the connection point mayinclude a connector 719, such as a hinge or link, which allows the lever710 to move relative to the acoustic diaphragm 702, thereby to allow theacoustic diaphragm 702 to move in a pistonic motion (arrow 718), ratherthan following the arcuate path of the lever 710.

FIGS. 14, 15, 16A, and 16B illustrate one implementation of the movingmagnet motor 712 (FIG. 16A) for applying force to the lever 710. Withreference to FIG. 14, in the illustrated implementation, the movingmagnet motor 712 includes a substantially planar armature 720 that isattached to the lever 710. The armature 720 includes a single permanentmagnet 722. The armature 720 and the lever 710 may be part of oneunitary structure.

Referring to FIG. 15, the moving magnet motor 712 also includes a stator724 that includes a pair of cores 726. The cores 726 are formed of highmagnetic permeability material, such as soft iron. Each core 726includes a first leg 728, a second leg 730, and a back portion 732 thatextends between the first and second legs 728, 730. The first leg 728,the second leg 730, and the back portion 732 can be formed as separatecomponents that are fastened together or can be integrally formed out ofa common piece of material.

Each core 726 also includes a coil 734 of electrically conductivematerial wound about the back portion 732 of the associated core 726between the first and second legs 728, 730. In this regard, the cores726 are said to include a backside winding, which, by keeping the coils734 out of the vertical stack-up of components, helps to provide thestator 724 with a low profile height for an overall lower profileloudspeaker 700. The cores 726 are arranged adjacent to each other anddefine an air gap 736 therebetween, within which the armature 720 issuspended.

Notably, the cores 726 together define a pair of poles 738 a, 738 b forthe single permanent magnet 722 of the armature 720 to interact with.The first legs 728 of the cores 726 form a first pole 738 a with a firstpair of opposed pole faces 740 a and the second legs 730 form a secondpole 738 b with a second pair of opposed pole faces 740 b. The air gap736 separates the first pair of opposed pole faces 740 a, as well as thesecond pair of opposed pole faces 740 b.

The coils 734 are arranged so that the magnetic fields produced bycurrent flowing through them add constructively. Current in coils 734produces a magnetic flux across the air gap 736. As illustrated in FIG.16B, the current in the coils 734 produces magnetic flux which passesacross the air gap 736 in two opposing directions at the same time. Thatis, magnetic flux 742 produced by the current in the coils 734 passes ina first direction between the first pair opposed pole faces 740 a,while, at the same time, passing in a second direction, opposite thefirst direction, between the second pair of opposed pole faces 740 b.The flow of current in the coils 734 is reversed to reverse thedirection of the magnetic flux. The magnetic flux interacts with thepermanent magnet 722 in the armature 720 (i.e., attracting the permanentmagnet to either the first or the second pole depending on the directionof current flow in the coils) to drive the motion of the acousticdiaphragm 702. The flow of current in the coils 734 can be repeatedlyreversed to drive the armature 720 in oscillatory motion. Theinteraction of the magnetic field in the air gap 736 due to currentflowing in the coils 734 and magnetic field of the magnet 722 applyforce to the magnet 722 in a non-contact manner. Force from the magnet722 is coupled structurally to the lever 710 and ultimately to theacoustic diaphragm 702.

The two pole stator/one magnet arrangement of the moving magnet motor712 provides a substantially zero detent topology. That is, with thistwo pole/one magnet configuration substantially no cogging (detent)forces are generated between the stator 724 and the permanent magnet 722as the lever 710 is driven in oscillatory rotary motion; i.e., thedetent forces are less than 10% of the work needed to move the acousticdiaphragm 702 over its peak-to-peak excursion distance (e.g., less than5% of the work needed to move the acoustic diaphragm 702). This can helpto minimize power consumption since the motor does not have to work toovercome its own detent forces. This can be particularly beneficialwhere the loudspeaker 700 is configured as a sealed box (i.e., where theenclosure 704 is sealed). In such sealed box configurations, the motorneeds to overcome the sum of the box stiffness and the magnetic detentstiffness. Reducing the detent stiffness can significantly reduce thepower needed to drive the motor.

Although FIGS. 12A and 12B illustrate a diaphragm driven by a singlelever, in some cases, multiples of such levers, each having anassociated moving magnet motor, can be used for driving the diaphragm.

A number of implementations have been described. Nevertheless, it willbe understood that additional modifications may be made withoutdeparting from the spirit and scope of the inventive concepts describedherein, and, accordingly, other embodiments are within the scope of thefollowing claims.

What is claimed is:
 1. An apparatus comprising: I.) a load; II.) a lever coupled to the load; and III.) an electric motor coupled to the lever for driving the lever in oscillatory, rotary motion about a pivot axis, the electric motor comprising: A.) an armature comprising a permanent magnet, the armature being coupled to the lever; and B.) a stator defining an air gap within which the armature is disposed, the stator being configured for creating magnetic flux across the air gap for the permanent magnet to interact with, thereby to drive motion of the load, wherein the electric motor is configured such that substantially no detent forces are generated between the stator and the permanent magnet as the lever is driven by the motor, wherein the stator is configured to generate magnetic flux which passes across the air gap in two opposing directions at the same time.
 2. The apparatus of claim 1, wherein the stator defines: a first pole including a first pair of opposed pole faces, and a second pole including a second pair of opposed pole faces, and wherein the air gap separates the first pair of opposed pole faces, and the gap separates the second pair of opposed pole faces.
 3. The apparatus of claim 2, wherein the stator is configured to generate magnetic flux which passes in a first one of the two opposing directions between the first pair opposed pole faces, while, at the same time, passing in a second one of the two opposing directions, opposite the first one of the two opposing directions, between the second pair of opposed pole faces.
 4. The apparatus of claim 1, wherein the stator comprises: a pair of cores of high magnetic permeability material, the cores together defining: a first pole; a second pole; and an air gap within which the permanent magnet is suspended; and a pair of coils, each coil wrapped around one of the cores for carrying current to generate magnetic flux across the air gap for the permanent magnet to interact with.
 5. The apparatus of claim 1, wherein the lever is coupled to the load such that oscillatory, rotary motion of the lever moves the load in a pistonic motion.
 6. The apparatus of claim 1, wherein the apparatus is a loudspeaker, and wherein the load is an acoustic diaphragm.
 7. The apparatus of claim 6, wherein the loudspeaker has a sealed box construction.
 8. The apparatus of claim 6, wherein the lever is coupled to the acoustic diaphragm such that oscillatory, rotary motion of the lever moves the acoustic diaphragm in a pistonic motion.
 9. A loudspeaker comprising: I.) an acoustic diaphragm; and II.) an electric motor coupled to the acoustic diaphragm for driving motion of the acoustic diaphragm, the electric motor comprising: A.) a stator comprising: i.) a pair of cores of high magnetic permeability material, the cores together defining: a.) a first pole, b.) a second pole, and c.) an air gap separating opposed faces of the first and second poles; ii.) a pair of coils, each coil wrapped around one of the cores for carrying current to generate magnetic flux across the air gap; and B.) an armature comprising a single permanent magnet, the armature disposed within the air gap in non-contacting relationship with the stator and supported to allow the permanent magnet to interact with magnet flux in the air gap for moving the armature between the first and second poles, wherein the stator is configured to generate magnetic flux which passes across the air gap in two opposing directions at the same time.
 10. The loudspeaker of claim 9, wherein the stator is configured to generate magnetic flux which passes in a first one of the two opposing directions between opposed pole faces of the first pole, while, at the same time, passing in a second one of the two opposing directions, opposite the first one of the two opposing directions, between opposed pole faces of the second pole.
 11. The loudspeaker of claim 9, wherein the stator is configured to generate magnetic flux across the air gap such that the permanent magnet is attracted to one of the first and second poles and is repelled by the other one of the first and second poles. 